Threshold systems of conventional construction are often inefficient in preventing air and water from infiltrating toward the interior of a dwelling since, in most of these designs, the sealing effect is obtained by application of a single weather-strip against a mating surface. However, when strong winds prevail, the pressure difference between the exterior and the interior of the dwelling contributes to detach the weather-strip from its mating surface, thus forming a passage allowing water droplets and cold air to penetrate the dwelling. This passage being relatively small, the cold air mass passes with a high velocity, further contributing to entrain water droplets toward the interior of the dwelling.